1 Why Write Tests for your Rails Applications?

Rails makes it super easy to write your tests. It starts by producing skeleton test code while you are creating your models and controllers.

By simply running your Rails tests you can ensure your code adheres to the desired functionality even after some major code refactoring.

Rails tests can also simulate browser requests and thus you can test your application's response without having to test it through your browser.

2 Introduction to Testing

Testing support was woven into the Rails fabric from the beginning. It wasn't an "oh! let's bolt on support for running tests because they're new and cool" epiphany. Just about every Rails application interacts heavily with a database and, as a result, your tests will need a database to interact with as well. To write efficient tests, you'll need to understand how to set up this database and populate it with sample data.

2.1 The Test Environment

By default, every Rails application has three environments: development, test, and production. The database for each one of them is configured in config/database.yml.

A dedicated test database allows you to set up and interact with test data in isolation. Tests can mangle test data with confidence, that won't touch the data in the development or production databases.

2.2 Rails Sets up for Testing from the Word Go

Rails creates a test folder for you as soon as you create a Rails project using rails newapplication_name. If you list the contents of this folder then you shall see:

The models directory is meant to hold tests for your models, the controllers directory is meant to hold tests for your controllers and the integration directory is meant to hold tests that involve any number of controllers interacting.

Fixtures are a way of organizing test data; they reside in the fixtures folder.

The test_helper.rb file holds the default configuration for your tests.

2.3 The Low-Down on Fixtures

For good tests, you'll need to give some thought to setting up test data. In Rails, you can handle this by defining and customizing fixtures.

2.3.1 What Are Fixtures?

Fixtures is a fancy word for sample data. Fixtures allow you to populate your testing database with predefined data before your tests run. Fixtures are database independent written in YAML. There is one file per model.

You'll find fixtures under your test/fixtures directory. When you run rails generate model to create a new model fixture stubs will be automatically created and placed in this directory.

2.3.2 YAML

YAML-formatted fixtures are a very human-friendly way to describe your sample data. These types of fixtures have the .yml file extension (as in users.yml).

Each fixture is given a name followed by an indented list of colon-separated key/value pairs. Records are typically separated by a blank space. You can place comments in a fixture file by using the # character in the first column. Keys which resemble YAML keywords such as 'yes' and 'no' are quoted so that the YAML Parser correctly interprets them.

If you are working with associations, you can simply
define a reference node between two different fixtures. Here's an example with
a belongs_to/has_many association:

2.3.3 ERB'in It Up

ERB allows you to embed Ruby code within templates. The YAML fixture format is pre-processed with ERB when Rails loads fixtures. This allows you to use Ruby to help you generate some sample data. For example, the following code generates a thousand users:

2.3.4 Fixtures in Action

Rails by default automatically loads all fixtures from the test/fixtures folder for your models and controllers test. Loading involves three steps:

Remove any existing data from the table corresponding to the fixture

Load the fixture data into the table

Dump the fixture data into a variable in case you want to access it directly

2.3.5 Fixtures are Active Record objects

Fixtures are instances of Active Record. As mentioned in point #3 above, you can access the object directly because it is automatically setup as a local variable of the test case. For example:

# this will return the User object for the fixture named david
users(:david)
# this will return the property for david called id
users(:david).id
# one can also access methods available on the User class
email(david.girlfriend.email, david.location_tonight)

3 Unit Testing your Models

In Rails, models tests are what you write to test your models.

For this guide we will be using Rails scaffolding. It will create the model, a migration, controller and views for the new resource in a single operation. It will also create a full test suite following Rails best practices. I will be using examples from this generated code and will be supplementing it with additional examples where necessary.

A line by line examination of this file will help get you oriented to Rails testing code and terminology.

require 'test_helper'

As you know by now, test_helper.rb specifies the default configuration to run our tests. This is included with all the tests, so any methods added to this file are available to all your tests.

class PostTest < ActiveSupport::TestCase

The PostTest class defines a test case because it inherits from ActiveSupport::TestCase. PostTest thus has all the methods available from ActiveSupport::TestCase. You'll see those methods a little later in this guide.

Any method defined within a class inherited from MiniTest::Unit::TestCase
(which is the superclass of ActiveSupport::TestCase) that begins with test (case sensitive) is simply called a test. So, test_password, test_valid_password and testValidPassword all are legal test names and are run automatically when the test case is run.

Rails adds a test method that takes a test name and a block. It generates a normal MiniTest::Unit test with method names prefixed with test_. So,

test "the truth" do
assert true
end

acts as if you had written

def test_the_truth
assert true
end

only the test macro allows a more readable test name. You can still use regular method definitions though.

The method name is generated by replacing spaces with underscores. The result does not need to be a valid Ruby identifier though, the name may contain punctuation characters etc. That's because in Ruby technically any string may be a method name. Odd ones need define_method and send calls, but formally there's no restriction.

assert true

This line of code is called an assertion. An assertion is a line of code that evaluates an object (or expression) for expected results. For example, an assertion can check:

does this value = that value?

is this object nil?

does this line of code throw an exception?

is the user's password greater than 5 characters?

Every test contains one or more assertions. Only when all the assertions are successful will the test pass.

3.1 Preparing your Application for Testing

Before you can run your tests, you need to ensure that the test database structure is current. For this you can use the following rake commands:

$ rake db:migrate
...
$ rake db:test:load

The rake db:migrate above runs any pending migrations on the development environment and updates db/schema.rb. The rake db:test:load recreates the test database from the current db/schema.rb. On subsequent attempts, it is a good idea to first run db:test:prepare, as it first checks for pending migrations and warns you appropriately.

db:test:prepare will fail with an error if db/schema.rb doesn't exist.

3.1.1 Rake Tasks for Preparing your Application for Testing

Tasks

Description

rake db:test:clone

Recreate the test database from the current environment's database schema

rake db:test:clone_structure

Recreate the test database from the development structure

rake db:test:load

Recreate the test database from the current schema.rb

rake db:test:prepare

Check for pending migrations and load the test schema

rake db:test:purge

Empty the test database.

You can see all these rake tasks and their descriptions by running rake --tasks --describe

3.2 Running Tests

Running a test is as simple as invoking the file containing the test cases through rake test command.

In the output, F denotes a failure. You can see the corresponding trace shown under 1) along with the name of the failing test. The next few lines contain the stack trace followed by a message which mentions the actual value and the expected value by the assertion. The default assertion messages provide just enough information to help pinpoint the error. To make the assertion failure message more readable, every assertion provides an optional message parameter, as shown here:

test "should not save post without title" do
post = Post.new
assert !post.save, "Saved the post without a title"
end

Running this test shows the friendlier assertion message:

1) Failure:
test_should_not_save_post_without_title(PostTest) [test/models/post_test.rb:6]:
Saved the post without a title

Now to get this test to pass we can add a model level validation for the title field.

Now, if you noticed, we first wrote a test which fails for a desired functionality, then we wrote some code which adds the functionality and finally we ensured that our test passes. This approach to software development is referred to as Test-Driven Development (TDD).

Many Rails developers practice Test-Driven Development (TDD). This is an excellent way to build up a test suite that exercises every part of your application. TDD is beyond the scope of this guide, but one place to start is with 15 TDD steps to create a Rails application.

To see how an error gets reported, here's a test containing an error:

test "should report error" do
# some_undefined_variable is not defined elsewhere in the test case
some_undefined_variable
assert true
end

Now you can see even more output in the console from running the tests:

The execution of each test method stops as soon as any error or an assertion failure is encountered, and the test suite continues with the next method. All test methods are executed in alphabetical order.

3.3 What to Include in Your Unit Tests

Ideally, you would like to include a test for everything which could possibly break. It's a good practice to have at least one test for each of your validations and at least one test for every method in your model.

3.4 Available Assertions

By now you've caught a glimpse of some of the assertions that are available. Assertions are the worker bees of testing. They are the ones that actually perform the checks to ensure that things are going as planned.

There are a bunch of different types of assertions you can use.
Here's an extract of the assertions you can use with minitest, the default testing library used by Rails. The [msg] parameter is an optional string message you can specify to make your test failure messages clearer. It's not required.

Assertion

Purpose

assert( test, [msg] )

Ensures that test is true.

assert_not( test, [msg] )

Ensures that test is false.

assert_equal( expected, actual, [msg] )

Ensures that expected == actual is true.

assert_not_equal( expected, actual, [msg] )

Ensures that expected != actual is true.

assert_same( expected, actual, [msg] )

Ensures that expected.equal?(actual) is true.

assert_not_same( expected, actual, [msg] )

Ensures that expected.equal?(actual) is false.

assert_nil( obj, [msg] )

Ensures that obj.nil? is true.

assert_not_nil( obj, [msg] )

Ensures that obj.nil? is false.

assert_match( regexp, string, [msg] )

Ensures that a string matches the regular expression.

assert_no_match( regexp, string, [msg] )

Ensures that a string doesn't match the regular expression.

assert_in_delta( expecting, actual, [delta], [msg] )

Ensures that the numbers expected and actual are within delta of each other.

assert_not_in_delta( expecting, actual, [delta], [msg] )

Ensures that the numbers expected and actual are not within delta of each other.

assert_throws( symbol, [msg] ) { block }

Ensures that the given block throws the symbol.

assert_raises( exception1, exception2, ... ) { block }

Ensures that the given block raises one of the given exceptions.

assert_nothing_raised( exception1, exception2, ... ) { block }

Ensures that the given block doesn't raise one of the given exceptions.

assert_instance_of( class, obj, [msg] )

Ensures that obj is an instance of class.

assert_not_instance_of( class, obj, [msg] )

Ensures that obj is not an instance of class.

assert_kind_of( class, obj, [msg] )

Ensures that obj is or descends from class.

assert_not_kind_of( class, obj, [msg] )

Ensures that obj is not an instance of class and is not descending from it.

assert_respond_to( obj, symbol, [msg] )

Ensures that obj responds to symbol.

assert_not_respond_to( obj, symbol, [msg] )

Ensures that obj does not respond to symbol.

assert_operator( obj1, operator, [obj2], [msg] )

Ensures that obj1.operator(obj2) is true.

assert_not_operator( obj1, operator, [obj2], [msg] )

Ensures that obj1.operator(obj2) is false.

assert_send( array, [msg] )

Ensures that executing the method listed in array[1] on the object in array[0] with the parameters of array[2 and up] is true. This one is weird eh?

flunk( [msg] )

Ensures failure. This is useful to explicitly mark a test that isn't finished yet.

Because of the modular nature of the testing framework, it is possible to create your own assertions. In fact, that's exactly what Rails does. It includes some specialized assertions to make your life easier.

Creating your own assertions is an advanced topic that we won't cover in this tutorial.

3.5 Rails Specific Assertions

Rails adds some custom assertions of its own to the test/unit framework:

Assertion

Purpose

assert_difference(expressions, difference = 1, message = nil) {...}

Test numeric difference between the return value of an expression as a result of what is evaluated in the yielded block.

assert_no_difference(expressions, message = nil, &amp;block)

Asserts that the numeric result of evaluating an expression is not changed before and after invoking the passed in block.

assert_recognizes(expected_options, path, extras={}, message=nil)

Asserts that the routing of the given path was handled correctly and that the parsed options (given in the expected_options hash) match path. Basically, it asserts that Rails recognizes the route given by expected_options.

Asserts that the provided options can be used to generate the provided path. This is the inverse of assert_recognizes. The extras parameter is used to tell the request the names and values of additional request parameters that would be in a query string. The message parameter allows you to specify a custom error message for assertion failures.

assert_response(type, message = nil)

Asserts that the response comes with a specific status code. You can specify :success to indicate 200-299, :redirect to indicate 300-399, :missing to indicate 404, or :error to match the 500-599 range

assert_redirected_to(options = {}, message=nil)

Assert that the redirection options passed in match those of the redirect called in the latest action. This match can be partial, such that assert_redirected_to(controller: "weblog") will also match the redirection of redirect_to(controller: "weblog", action: "show") and so on.

assert_template(expected = nil, message=nil)

Asserts that the request was rendered with the appropriate template file.

You'll see the usage of some of these assertions in the next chapter.

4 Functional Tests for Your Controllers

In Rails, testing the various actions of a single controller is called writing functional tests for that controller. Controllers handle the incoming web requests to your application and eventually respond with a rendered view.

4.1 What to Include in your Functional Tests

You should test for things such as:

was the web request successful?

was the user redirected to the right page?

was the user successfully authenticated?

was the correct object stored in the response template?

was the appropriate message displayed to the user in the view?

Now that we have used Rails scaffold generator for our Post resource, it has already created the controller code and tests. You can take look at the file posts_controller_test.rb in the test/controllers directory.

Let me take you through one such test, test_should_get_index from the file posts_controller_test.rb.

Note that you cannot test for template and layout at the same time, with one call to assert_template method.
Also, for the layout test, you can give a regular expression instead of a string, but using the string, makes
things clearer. On the other hand, you have to include the "layouts" directory name even if you save your layout
file in this standard layout directory. Hence,

assert_template layout: "application"

will not work.

If your view renders any partial, when asserting for the layout, you have to assert for the partial at the same time.
Otherwise, assertion will fail.

4.8 Testing Views

Testing the response to your request by asserting the presence of key HTML elements and their content is a useful way to test the views of your application. The assert_select assertion allows you to do this by using a simple yet powerful syntax.

You may find references to assert_tag in other documentation, but this is now deprecated in favor of assert_select.

There are two forms of assert_select:

assert_select(selector, [equality], [message]) ensures that the equality condition is met on the selected elements through the selector. The selector may be a CSS selector expression (String), an expression with substitution values, or an HTML::Selector object.

assert_select(element, selector, [equality], [message]) ensures that the equality condition is met on all the selected elements through the selector starting from the element (instance of HTML::Node) and its descendants.

For example, you could verify the contents on the title element in your response with:

assert_select 'title', "Welcome to Rails Testing Guide"

You can also use nested assert_select blocks. In this case the inner assert_select runs the assertion on the complete collection of elements selected by the outer assert_select block:

assert_select 'ul.navigation' do
assert_select 'li.menu_item'
end

Alternatively the collection of elements selected by the outer assert_select may be iterated through so that assert_select may be called separately for each element. Suppose for example that the response contains two ordered lists, each with four list elements then the following tests will both pass.

assert_select "ol" do |elements|
elements.each do |element|
assert_select element, "li", 4
end
end
assert_select "ol" do
assert_select "li", 8
end

The assert_select assertion is quite powerful. For more advanced usage, refer to its documentation.

4.8.1 Additional View-Based Assertions

There are more assertions that are primarily used in testing views:

Assertion

Purpose

assert_select_email

Allows you to make assertions on the body of an e-mail.

assert_select_encoded

Allows you to make assertions on encoded HTML. It does this by un-encoding the contents of each element and then calling the block with all the un-encoded elements.

css_select(selector) or css_select(element, selector)

Returns an array of all the elements selected by the selector. In the second variant it first matches the base element and tries to match the selector expression on any of its children. If there are no matches both variants return an empty array.

Here's an example of using assert_select_email:

assert_select_email do
assert_select 'small', 'Please click the "Unsubscribe" link if you want to opt-out.'
end

5 Integration Testing

Integration tests are used to test the interaction among any number of controllers. They are generally used to test important work flows within your application.

Unlike Unit and Functional tests, integration tests have to be explicitly created under the 'test/integration' folder within your application. Rails provides a generator to create an integration test skeleton for you.

Integration tests inherit from ActionDispatch::IntegrationTest. This makes available some additional helpers to use in your integration tests. Also you need to explicitly include the fixtures to be made available to the test.

5.1 Helpers Available for Integration Tests

In addition to the standard testing helpers, there are some additional helpers available to integration tests:

Helper

Purpose

https?

Returns true if the session is mimicking a secure HTTPS request.

https!

Allows you to mimic a secure HTTPS request.

host!

Allows you to set the host name to use in the next request.

redirect?

Returns true if the last request was a redirect.

follow_redirect!

Follows a single redirect response.

request_via_redirect(http_method, path, [parameters], [headers])

Allows you to make an HTTP request and follow any subsequent redirects.

post_via_redirect(path, [parameters], [headers])

Allows you to make an HTTP POST request and follow any subsequent redirects.

get_via_redirect(path, [parameters], [headers])

Allows you to make an HTTP GET request and follow any subsequent redirects.

patch_via_redirect(path, [parameters], [headers])

Allows you to make an HTTP PATCH request and follow any subsequent redirects.

put_via_redirect(path, [parameters], [headers])

Allows you to make an HTTP PUT request and follow any subsequent redirects.

delete_via_redirect(path, [parameters], [headers])

Allows you to make an HTTP DELETE request and follow any subsequent redirects.

As you can see the integration test involves multiple controllers and exercises the entire stack from database to dispatcher. In addition you can have multiple session instances open simultaneously in a test and extend those instances with assertion methods to create a very powerful testing DSL (domain-specific language) just for your application.

Here's an example of multiple sessions and custom DSL in an integration test

6 Rake Tasks for Running your Tests

You don't need to set up and run your tests by hand on a test-by-test basis.
Rails comes with a number of commands to help in testing.
The table below lists all commands that come along in the default Rakefile
when you initiate a Rails project.

Tasks

Description

rake test

Runs all unit, functional and integration tests. You can also simply run rake as Rails will run all the tests by default

rake test:controllers

Runs all the controller tests from test/controllers

rake test:functionals

Runs all the functional tests from test/controllers, test/mailers, and test/functional

rake test:helpers

Runs all the helper tests from test/helpers

rake test:integration

Runs all the integration tests from test/integration

rake test:mailers

Runs all the mailer tests from test/mailers

rake test:models

Runs all the model tests from test/models

rake test:units

Runs all the unit tests from test/models, test/helpers, and test/unit

rake test:all

Runs all tests quickly by merging all types and not resetting db

rake test:all:db

Runs all tests quickly by merging all types and resetting db

There're also some test commands which you can initiate by running rake tasks:

Tasks

Description

rake test

Runs all unit, functional and integration tests. You can also simply run rake as the test target is the default.

rake test:recent

Tests recent changes

rake test:uncommitted

Runs all the tests which are uncommitted. Supports Subversion and Git

7 Brief Note About MiniTest

Ruby ships with a boat load of libraries. Ruby 1.8 provides Test::Unit, a framework for unit testing in Ruby. All the basic assertions discussed above are actually defined in Test::Unit::Assertions. The class ActiveSupport::TestCase which we have been using in our unit and functional tests extends Test::Unit::TestCase, allowing
us to use all of the basic assertions in our tests.

Ruby 1.9 introduced MiniTest, an updated version of Test::Unit which provides a backwards compatible API for Test::Unit. You could also use MiniTest in Ruby 1.8 by installing the minitest gem.

8 Setup and Teardown

If you would like to run a block of code before the start of each test and another block of code after the end of each test you have two special callbacks for your rescue. Let's take note of this by looking at an example for our functional test in Posts controller:

require 'test_helper'
class PostsControllerTest < ActionController::TestCase
# called before every single test
def setup
@post = posts(:one)
end
# called after every single test
def teardown
# as we are re-initializing @post before every test
# setting it to nil here is not essential but I hope
# you understand how you can use the teardown method
@post = nil
end
test "should show post" do
get :show, id: @post.id
assert_response :success
end
test "should destroy post" do
assert_difference('Post.count', -1) do
delete :destroy, id: @post.id
end
assert_redirected_to posts_path
end
end

Above, the setup method is called before each test and so @post is available for each of the tests. Rails implements setup and teardown as ActiveSupport::Callbacks. Which essentially means you need not only use setup and teardown as methods in your tests. You could specify them by using:

a block

a method (like in the earlier example)

a method name as a symbol

a lambda

Let's see the earlier example by specifying setup callback by specifying a method name as a symbol:

10 Testing Your Mailers

Testing mailer classes requires some specific tools to do a thorough job.

10.1 Keeping the Postman in Check

Your mailer classes — like every other part of your Rails application — should be tested to ensure that it is working as expected.

The goals of testing your mailer classes are to ensure that:

emails are being processed (created and sent)

the email content is correct (subject, sender, body, etc)

the right emails are being sent at the right times

10.1.1 From All Sides

There are two aspects of testing your mailer, the unit tests and the functional tests. In the unit tests, you run the mailer in isolation with tightly controlled inputs and compare the output to a known value (a fixture.) In the functional tests you don't so much test the minute details produced by the mailer; instead, we test that our controllers and models are using the mailer in the right way. You test to prove that the right email was sent at the right time.

10.2 Unit Testing

In order to test that your mailer is working as expected, you can use unit tests to compare the actual results of the mailer with pre-written examples of what should be produced.

10.2.1 Revenge of the Fixtures

For the purposes of unit testing a mailer, fixtures are used to provide an example of how the output should look. Because these are example emails, and not Active Record data like the other fixtures, they are kept in their own subdirectory apart from the other fixtures. The name of the directory within test/fixtures directly corresponds to the name of the mailer. So, for a mailer named UserMailer, the fixtures should reside in test/fixtures/user_mailer directory.

When you generated your mailer, the generator creates stub fixtures for each of the mailers actions. If you didn't use the generator you'll have to make those files yourself.

10.2.2 The Basic Test Case

Here's a unit test to test a mailer named UserMailer whose action invite is used to send an invitation to a friend. It is an adapted version of the base test created by the generator for an invite action.

In the test we send the email and store the returned object in the email
variable. We then ensure that it was sent (the first assert), then, in the
second batch of assertions, we ensure that the email does indeed contain what we
expect. The helper read_fixture is used to read in the content from this file.

Here's the content of the invite fixture:

Hi friend@example.com,
You have been invited.
Cheers!

This is the right time to understand a little more about writing tests for your
mailers. The line ActionMailer::Base.delivery_method = :test in
config/environments/test.rb sets the delivery method to test mode so that
email will not actually be delivered (useful to avoid spamming your users while
testing) but instead it will be appended to an array
(ActionMailer::Base.deliveries).

The ActionMailer::Base.deliveries array is only reset automatically in
ActionMailer::TestCase tests. If you want to have a clean slate outside Action
Mailer tests, you can reset it manually with:
ActionMailer::Base.deliveries.clear

10.3 Functional Testing

Functional testing for mailers involves more than just checking that the email body, recipients and so forth are correct. In functional mail tests you call the mail deliver methods and check that the appropriate emails have been appended to the delivery list. It is fairly safe to assume that the deliver methods themselves do their job. You are probably more interested in whether your own business logic is sending emails when you expect them to go out. For example, you can check that the invite friend operation is sending an email appropriately:

11 Testing helpers

In order to test helpers, all you need to do is check that the output of the
helper method matches what you'd expect. Tests related to the helpers are
located under the test/helpers directory. Rails provides a generator which
generates both the helper and the test file:

Feedback

You may also find incomplete content, or stuff that is not up to date.
Please do add any missing documentation for master. Make sure to check
Edge Guides first to verify
if the issues are already fixed or not on the master branch.
Check the Ruby on Rails Guides Guidelines
for style and conventions.

If for whatever reason you spot something to fix but cannot patch it yourself, please
open an issue.